1. Field of the Invention
The present invention relates to a light emitting device and a manufacturing method thereof and particularly to a light emitting device having LED (light emitting diode) elements mounted thereon and a manufacturing method thereof.
2. Description of the Related Art
Various types of light emitting devices, which have LED elements mounted thereon, are known in the art. One of them is a single-chip-type light emitting device. In the single chip configuration, one LED element is mounted in one package. Another type is a multi-chip configuration that has a plurality of LED elements mounted in one package. Still another type is a light emitting device that has red, green and blue LED elements in a single package. This type is called RGB three-in-one package.
For example, Japanese Patent Application Publication (Kokai) No. 2007-129062 discloses an LED light source device including resistors connected in parallel with LED elements. This LED light source device adjusts the resistance of the resistors to make the brightness or emission spectrum of the LED elements constant. This compensates for variations in brightness between the LED elements.
Because the emission brightness of LED elements depends on the crystallinity of their semiconductor epitaxial layer, it is difficult to make the emission brightness of the LED elements even all the time. Thus, as to the single-chip-type light emitting devices that have one LED element mounted in each package, variations in brightness occur between the light emitting devices. As to the multi-chip-type light emitting devices that have a plurality of LED elements mounted in one package, brightness unevenness occurs in one light emitting device. As to white LEDs of the RGB three-in-one package type, the brightness ratio of R:G:B cannot be an appropriate ratio, and thus white light is different in tone from one light emitting device to another light emitting device. As to white LEDs that are constituted by a combination of a blue LED and a fluorescent substance, white light is different in tone from one light emitting device to another light emitting device.